#include<cstdio>
using namespace std;
char p[2000000010];
int n,i,j,cnt;
int main()
{
    freopen("ciur.in","r",stdin);
    freopen("ciur.out","w",stdout);
    scanf("%d",&n);
    cnt++;
    for(i=3;i*i<=n;i+=2)
    if(!p[i])
    {
        cnt++;
        for(j=i*i;j<=n;j+=2*i) p[j]=1;
    }
    for(;i<=n;i+=2)
        if(!p[i]) cnt++;
    printf("%d\n",cnt);
    return 0;
}